1. Field of the Invention
The present invention relates to methods for removing a silicon-oxy-nitride layer from a semiconductor substrate and wafer surface cleaning, and more particularly to methods for removing a silicon-oxy-nitride layer without residual oxide and wafer surface cleaning.
2. Description of the Related Art
Silicon oxy-nitride (SiOXNY) layers formed over polysilicon layers used as gate electrodes in semiconductor devices are commonly used as bottom anti-reflective coating (BARC) layers. The BARC layers are formed over the polysilicon layers before forming photoresist layers used to define the gate electrodes, and they prevent reflection of actinic light used to expose the photoresist layers from their surfaces. The processing set forth is extremely crucial for the manufacturing techniques of very large scale integrated circuit (VLSI) and ultra large scale integrated circuit (ULSI). After the lithography process defines the gate electrodes, the silicon-oxy-nitride layer is removed using a dry etching process or a wet etching process using a heated phosphorus acid (H3PO4) solution. In addition, when the quality of the deposited silicon-oxy-nitride layer is unqualified, the silicon-oxy-nitride layer must be removed completely using the heated H3PO4 solution. However, the silicon-oxy-nitride layer is usually difficult to remove completely as it contains oxide composition. Furthermore, plasma of the dry etching process may cause undesired damage that may induce device failure. Therefore, it is very necessary to provide a new option to remove the silicon-oxy-nitride layers without the problems mentioned above.
Standard clean 1 (SC1) or RCA1 and standard clean 2 (SC2) or RCA2 are almost the standard cleaning techniques and recipes throughout integrated circuit processing. The SC1 solution comprises a hot aqueous mixture of ammonium hydroxide, hydrogen peroxide, and water (1:1:5 of 30%. H2O2, 28% NH4OH and H2O) and the SC2 solution comprises a hot acid mixture of hydrogen peroxide, hydrochloric acid and water (1:1:5 of 30% H2O2, 37% HCl and H2O). Both the SC1 and SC2 solutions contain hydrogen peroxide, which easily reacts with silicon atoms of the wafer surface to form chemical oxide layers. Usually, these chemical oxide layers are removed using dilute hydrofluoric (DHF) acid, but the DHF acid causes the formation of a hydrogen-terminated or hydrogen-passivated layer. The undesired hydrogen-terminated layer is hydrophobic and susceptible to particle contamination which will result in defects in the following formed films.
The hydrogen-passivated layer easily causes the formation of a native oxide layer when a wafer is exposed to the atmosphere. Especially during wafer transport in the clean room or reactor pump down, silicon atoms of the wafer surface having dangling bonds will adsorb hydrogen atoms to form a hydrophobic hydrogen-terminated surface. In this manner, oxygen will bond with silicon atoms to form an undesired native oxide layer. FIG. 1A shows the growth of the native oxide layer on a hydrogen-terminated surface of a silicon wafer exposed in the atmosphere. Besides, as a wafer is immersed in water or rinsed by deionized (DI) water, hydroxyl or oxygen atom will bond with silicon atoms of the wafer surface to form an oxygen-terminated or hydroxyl-terminated layer as shown in FIG. 1B. Silicon-hydroxyl groups formed by physically adsorbed water molecules undergoing dissociative chemisorption on silicon atoms act as adsorption sites for additional water molecules and result in further oxidation.
After performing wafer surface cleaning procedures by using the SC1 and SC2 solutions to clean wafers or the DHF acid to remove the native oxide and the chemical oxide, DI water is often used sequentially by the semiconductor industry to rinse the wafers. According to the phenomenon mentioned above, a native oxide layer is very likely formed again after performing the standard or conventional wafer surface cleaning procedures. Moreover, in the following dry procedure, however, undesired contaminations, such as water marks, particles and even silicon powders may be induced. Therefore, it is necessary to provide a new wafer surface cleaning method to replace the conventional one without the problems set forth.
It is therefore an object of the invention to provide a mixture solution of ethylene glycol (EG) and hydrogen fluoride (HF) to replace the conventional wet etching solution to completely remove a silicon-oxy-nitride layer containing oxide.
It is another object of this invention to provide a wet etching process used a mixture solution of ethylene glycol and hydrogen fluoride to replace the conventional dry etching process to remove silicon-oxy-nitride layer without plasma damages.
It is a further object of this invention to provide a method for wafer surface cleaning used a mixture solution of ethylene glycol and hydrogen fluoride to replace the conventional one used a solution of HF and H2O (Dilute HF Solution) to effectively reduce the formation of undesired hydrophobic hydrogen-terminated layers on the wafer surface, therefore avoid particle contaminations and water absorption.
It is another object of this invention to provide a method for wafer surface cleaning used a mixture solution of ethylene glycol and hydrogen fluoride to replace the conventional one used a solution of HF and H2O to reduce wafer surface roughness and prevent water marks.
To achieve these objects, and in accordance with the purpose of the invention the invention utilizes a solution of ethylene glycol and hydrogen fluoride to completely remove the silicon-oxy-nitride layer from a substrate without residual oxide. Moreover, the method for wafer surface cleaning also uses a solution of ethylene glycol and hydrogen fluoride to remove chemical oxide or native oxide from wafer surfaces and an ethylene glycol solvent to rinse the wafer surfaces.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.